This invention relates to a developing device for an electrophotographic copier having a developing tank provided with a developing roller and a toner stirrer roller. The invention also relates in particular to a developing device for a copier of the so-called clam shell type of which the main body can be separated into an openable upper part and a horizontal base part.
An exemplary prior art developing device for a copier is illustrated for the purpose of comparison in FIG. 1 wherein numeral 5 indicates a photoreceptor and a developing tank 1, typically made of a metallic material, is disposed adjacent thereto. A developing roller (or magnet roller) 2 is supported inside the developing tank 1 on the side proximal to the photoreceptor 5 and a sensor for toner concentration 3 is affixed to the bottom plate la of the developing tank 1 below the developing roller 2. A toner stirrer roller 4 is supported inside the tank 1 on the distal side from the photoreceptor 5. The developing tank 1 is filled with a specified amount of developing agent 7 which may comprise only of toner (in the case of a single-component developing agent) or of toner and a carrier (in the case of a two-component developing agent). Numeral 6 indicates a doctor blade for regulating the thickness of the developing agent 7 attached onto the developing roller 2. If the developing agent 7 becomes insufficient or its lifetime has passed, the developing tank 1 which has been in use is discarded and is replaced by a new one. When a developing tank 1 is thus discarded, the developing roller 2, the toner concentration sensor 3 and the toner stirrer roller 4 which are attached to the tank 1 are also discarded at the same time.
Among the components of the developing device supported by or attached to the developing tank 1, the developing roller 2 and the toner concentration sensor 3 are relatively expensive and their lifetimes are longer than the lifetime of the developing agent 7. In other words, it is not economical to throw away these expensive components together with the developing agent 7 which has been spent.
The developing device described above may be disengageably attached to the housing of the copier (or a main frame supporting the housing) directly or, as shown schematically in FIG. 2, attached to and made a part of a much larger developing unit 80 including a case 81 which contains therein not only the aforementioned developing device but also the photoreceptor 5, a cleaning device 86, etc. In FIG. 2 which is a schematic sectional view of a copier of this type, numeral 78 indicates an optical unit, numeral 79 indicates a paper supplying device, numeral 82 indicates a fixing device and numeral 83 indicates a paper transporting device. If the developing agent 7 has been spent in a copier of this type, not only the spent developing agent 7 but also the photoreceptor 5 and the cleaning device 86, which may be still very much usable, are discarded with the case 8.